(1) Summary of the Invention
The invention relates to a vacuum cleaner and to a filter assembly therefor. It will be understood that the term "vacuum cleaner" is here used so as to encompass any type of cleaning apparatus which uses the creation of a vacuum to draw air along an airflow path.
(2) Description of Related Art
Vacuum cleaners of both the upright and cylinder types operate by utilizing a motor or fan unit to draw air along an airflow path from a dirty air inlet to a clean air outlet via some sort of filtering or dirt/dust separating apparatus. The air which passes along the airflow path thus passes through the motor or fan unit.
It is known to filter the air passing along the airflow path before it is expelled to the atmosphere. If the appropriate filter is located upstream of the motor or fan unit, any particles of dirt, carbon, etc. becoming entrained within the airflow inside the motor or fan unit will inevitably be expelled into the atmosphere with the airflow. If the filter is located downstream of the motor or fan unit, any dirt or dust remaining in the airflow after it has passed through the filtering or dirt/dust separating apparatus will pass through the motor or fan unit. This may cause the motor or fan unit to become unbalanced which will shorten its life and may result in premature failure. Also, dust can collect and build up in the region of the motor or fan unit which can result in sudden unwanted releases of large quantities of fine dust which can cause blockage of the filter or damage the motor or fan unit.
A very few manufacturers have, prior to the date of this application, been fitting electrostatic filters both before and after the motor or fan unit. This has the advantage of preventing dusty air from passing through the motor or fan unit and also of preventing any particles released within the motor or fan unit from escaping into the atmosphere. However, two problems have been identified in respect of this arrangement. Firstly, even if the operator remembers to change one of the filters, the second filter is rarely changed. Presumably this is because changing the first filter gives the operator sufficiently improved performance for the changing of the second filter to be thought unnecessary or else the second filter is forgotten. Secondly, the operator has difficulty in ascertaining that the filters require changing because they are not easily visible.
It is an object of the present invention to provide a vacuum cleaner having filters arranged both before and after the motor or fan unit which is easy and convenient to operate and to maintain.